The study of snow mechanics and snow pack failure (i.e. avalanches) has been of significant worldwide interest in the last two decades. However, efforts to quantitatively measure snow mechanics parameters in a "field" environment as opposed to a laboratory study have been relatively isolated. A real time avalanche surveillance system that accurately measures mechanical behaviour of a snow pack within the start zone and avalanche track of an avalanche hazard zone is not currently available. Most avalanche monitoring technologies focus on understanding the avalanche behaviour after snow pack failure. For example, descent velocities and times may be analyzed within the track, and sheer stresses, snow levels and moisture content of the snow pack within the start zone may be measured. The existing field avalanche monitoring techniques for assessment of snow pack failure consist of the following:
"Glide Shoe" Technique: This technique involves installing a series of "glide shoes" along a mountain face between the snow pack and the ground. The glide shoe resembles a single-pronged hook which grips the overlying snow pack and comprises a mobile element that moves with the snow. Each shoe is connected to a rotating potentiometer that comprises a static element fixed to the ground. As the shoe moves with the snow over the ground, a voltage change is registered which can be calibrated to an actual displacement reading. This technique is used for monitoring snow pack movements associated with glide avalanches.
Snow Profiling: This technique involves a person digging a shallow pit through the entire area of the snow pack, next to the avalanche-prone area. With the section of snow exposed, physical measurements are made of the snow pack layering, snow crystal shapes and sizes, density of layers, hardness of layers, and temperature, every 10 centimetres along the section. The data are evaluated to determine failure potential.
Snow Shear Test: This technique is used in conjunction with the snow profiling technique. A column of snow is isolated so as to be free-standing in a shallow pit. The blade of a shovel is inserted into the various snow layers and then slowly pulled out at a constant force. If the layer is weak, it will fail in shear as the shovel blade is removed. Although this technique is subjective, if the tester is experienced, the test can provide a good indication of the relative shear Strengths of the snow pack layers.
All of the existing techniques suffer from the drawback that they fail to provide real time continuous readings regarding changes occurring in the snow pack prior to and during the occurrence of an avalanche. As well, the prior art typically applies subjective, non-quantitative tests.
Studies of the mechanics of snow slab failure have shown that rates of movement (creep or glide), temperature and acoustic emissions within the Start zone of an avalanche slope are of interest in evaluating the stability of a snow pack. The rate of movement and temperature may serve as predictors of an avalanche event. On this basis, the applicants have developed a snow pack monitoring and surveillance system to enable the recording of snow pack transient movements, temperature and optionally acoustic emissions in real time. As well, it is desirable to provide a means for remotely detecting the occurrence of an avalanche and measuring its speed, by means of a detector, capable of withstanding an avalanche, installed within an avalanche track.
It is desirable-to provide a snow pack monitor that has one or more of the following benefits:
a) It should allow for the detection and measurement of movement of the entire snow pack relative to the slope base of the mountain.
b) It should allow for the detection and measurement of movement of the snow layers along weak layers within the snow pack which may indicate a shear failure mode such as typical of dry-slab avalanches.
c) It should allow for the vertical profiling of movement within the snow pack.
d) It should allow for the detection, measurement and profiling of temperature changes in the snow pack which may signal an impending avalanche.
e) The installation of the sensor probe should involve no disruption to the snow pack.
f) The monitoring and surveillance should be done remotely, outside the range of the avalanche and without danger to monitoring personnel.
g) The monitor should be adaptable to monitor actual avalanche activity in real time on an "indicator slope", i.e., a slope subject to frequent avalanches, where avalanche activity is indicative of avalanche risks generally in the region.